Customary international law increasingly being forced to adapt quickly to technology
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Custom can also develop rapidly based upon interpretations of treaties, as well as the rulings and declarations of international bodies and courts that can declare an existing customary rule.87 In the past 50 years, customary rules have developed quickly in response to technological innovation or in times of fundamental change.88 Moreover, rapid changes to custom do not require multiple instances of state practice,89 particularly when a state with special influence in the field seeks change.90 Most recently, the terrorist attacks on the World Trade Center and Pentagon resulted in changed custom concerning the use of force in self-defense against non-state actors91 and those who support or harbor terrorists.92 Such changes to the well-settled field of international humanitarian law would have been unthinkable in an earlier era.
Opponents of UNCLOS claim that the United States should not become a party because the United States already enjoys the benefits of UNCLOS through customary law and, therefore, should not unnecessarily incur the treaty's burdens. However, this ignores the fact that customary law can change and can also be influenced by how parties to UNCLOS decide to interpret its provisions.